Personnel in and on moving vehicles can be subjected to high acceleration environments, such as a crash or quick velocity change that give rise to rapid relative motion between the vehicle and the occupant. These environments create a risk of injury due to contact with vehicle or equipment structures, a risk of acceleration-related injury, and a risk of inadvertent ejection from the vehicle. The risk of injury is especially pronounced with personnel who cannot be restrained in a typical seat restraint system due to mobility requirements, such as with mobile aircrew members aboard the personnel/cargo bays of military helicopters.
Systems currently in use for restraining helicopter mobile aircrew include the gunner's belt with fixed-length tether, or an inertia reel-based system which locks an otherwise rotatable webbing spool upon excessive inertial input from the vehicle or upon excessive acceleration of webbing extraction. The drawbacks to the gunner's belt with a fixed-length tether are that the user is free to flail at any point within the sphere of reach of the tether. In a crash pulse or other acceleration input, the tether becomes suddenly taut and transmits the acceleration impulse directly to the user. As such, even though the tether may prevent the wearer from crashing into an interior fixture within the helicopter, the excessive g-forces that are exerted upon the user from the quick stop can still cause extensive injury.
The drawbacks to the inertia reel-based system are that the reel does not lock until an acceleration threshold is exceeded. This gives rise to unwanted webbing-type tether extraction and free travel. Once the webbing locks its length, the webbing becomes suddenly taut and transmits the acceleration impulse directly to the user, which can load the user with excessively high g-forces.
Both systems allow unwanted free travel of the user at high velocities relative to the vehicle, unwanted contact with vehicle structures at high velocity, possible inadvertent ejection or partial ejection from the vehicle due to unwanted free travel, and transmission of acceleration impulses to the user at the end of the travel. Both systems therefore give rise to contact injuries, acceleration injuries and compression injuries, as well as the dangers associated with travel outside the vehicle envelope.